1. Field of the Invention
This invention pertains to a method for replicating (copying) a multicolor hologram (e.g., a two-color hologram) into a photosensitive layer by masking to produce a copy (replicate) of the hologram in a manner such that the copy is an accurate and true replication of the hologram (e.g., master hologram) and the copy is characterized to possess a high brightness level and good color fidelity/purity comparable to that of the hologram that was replicated.
2. Description of Related Art
Replication by direct contact copying of a master hologram (either a reflection hologram or a transmission hologram) in which the master hologram is in direct contact with a photosensitive layer (e.g., a holographic recording film) is known from the art. With respect to reflection holograms, see, for example, the following references: 1) “Improved Process of Reflection Holography Replication and Heat Processing”, by D. F. Tipton, M. L. Armstrong, and S. H. Stevenson, Proc. SPIE, Vol. 2176, p 172-183 in Practical Holography VIII, Stephen A. Benton, Ed.; 2) “Photographic Reconstruction of the Optical Properties of an Object in its Own Scattered Radiation Field”, by Yu N. Denisyuk, Soviet Physics-Doklady, 7, pages 543-5 (1962); and 3) “Copying Reflection Holograms”, by Clark N. Kurtz, Journal of the Optical Society of America, 58, pages 856-7 (1968); each of these open literature references is incorporated by reference. Pertinent references in the patent literature include U.S. Pat. Nos. 4,995,685; 6,824,929; and 6,097,514, which are incorporated by reference. With respect to transmission holograms, see, for example, U.S. Pat. No. 4,209,250, which discloses a system for making multiple copies from a stationary planar transmission master hologram, and U.S. Pat. No. 4,973,113, which describes a method and apparatus for making a copy of a transmission hologram from a master. An additional open literature reference that covers copying of both reflection and transmission holograms is the replication portions of Chapter 20 of Optical Holography by R. J. Collier, C. B. Burchhardt and L. H. Lin, Academic Press (1971), which is incorporated by reference. The prior art teaches that such direct contact copying is done by contacting a photosensitive element, comprised of a photosensitive layer and a smooth coversheet, to a smooth master hologram such that a smooth surface of the coversheet is in direct contact with a smooth surface of the master hologram. It has been found that a method to make a multicolor hologram was needed. The present invention describes such a method.